<template>
	<ul class="list">
		<li 
		  class="item" 
		  v-for="item of letters" 
		  :key="item"
		  :ref="item"
		  @touchstart="handleTouchStart"
		  @touchmove="handleTouchMove"
		  @touchend="handleTouchEnd"
		  @click="handleLetterClick"
		>{{item}}</li>
	</ul>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props:{
		cities:Object
	},
	computed: {
		letters () {
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	updated () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e) {
			this.$emit('change',e.target.innerText)
		},
		handleTouchStart () {
			this.touchStatus = true
		},
		handleTouchMove (e) {
			if (this.touchStatus) {
				if (this.timer) {
					clearTimeout(this.timer)
				}
				this.timer = setTimeout(() => {
					// const startY = this.$refs['A'][0].offsetTop
				const touchY = e.touches[0].clientY - 79
				const index = Math.floor((touchY - this.startY) / 20)
				if (index >= 0 && index < this.letters.length)
				this.$emit('change',this.letters[index])
				},16)
			}
		},
		handleTouchEnd () {

		}
	}
}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
		display: flex
		flex-direction:column
		justify-content: center
		position: absolute
		top: 1.58rem
		right: 0
		bottom: 0
		width: .4rem
		.item
			text-align: center
			line-height: .4rem
			color: $bgColor
</style>